In 2004, ICQ users were enticed by a sales message from a supposed anti-virus vendor. On the vendor's site, a small program called Mitglieder was downloaded to the user's machine. The program enabled outsiders to infiltrate the user's machine. What type of malware is this an example of?

Trojan horse

Explanation:

Trojan, also known as Trojan horse is a type of malware that ensures that its users are misled of its true purpose. They are a common type of virus and are very dangerous in such a way that they can even hide within other programs that are harmless. Once installed, Trojan will infect every file on your computer and can even steal information or totally infiltrate your system.